1. Field of the Invention
The invention relates to an explosion relief valve for confined spaces, volumes or vessels, and more particularly for the crankcase of internal combustion engines, which includes a valve seat which may be fitted into a boundary wall of the space to be protected, a spring-loaded closure plate co-operating with the valve seat and at least one flame barrier having low pressure resistance installed in a gas path leading through the valve, which flame barrier preferably consists of sheet-metal strips stacked one above another transversely to the throughflow direction of the gas, which sheet-metal strips are preferably provided at least over part of their width with irregular corrugations, and at least one other perforated wall in the gas path.
2. The Prior Art
A valve of this kind is described in DE 1 126 676 C and GB-A-2 017 269. Two flame barriers, one disposed behind the other, are provided in the relief valves described therein, the British publication disclosing the combination of a sheet-metal ring stack with expanded metal fabric layers disposed thereafter. However, there is no mention whatsoever in that publication of structures which increase the mechanical stability and/or of affecting the flow characteristic.
A valve of an even simpler design is described in AT 311 129 and has very low conductance, a heat absorption capacity sufficient to prevent flames from passing through the valve being achieved without the application of vaporizable substances by means of the sheet-metal strips acting like cooling ribs. On the other hand, however, because of the substantially parallel sheet-metal strips, the flow resistance is not inadmissibly increased and the gas is able to flow away in a linear manner, with the result that the overpressure in the space protected by the valve can easily be reduced.
Particularly important as fields of application for explosion relief valves of this kind are the protection of confined spaces such as, for example, the crankcases of two-and four-stroke diesel engines, gas containers, fairly large pipelines and other spaces in which explosive substances are stored or in which highly inflammable gases may form. Several of the relief valves described may also be provided in parallel or in series.
It is desirable to provide a valve of the type specified in the introduction, in which a flame front is in every case reliably prevented from passing through the explosion relief valve for all fields of application, the throughflow of the valve is optimized, and the valve is also protected against mechanical damage, even after repeated explosions.
According to the invention, the perforated wall is made of an expanded metal strip. This material offers the facility of controllably influencing the flow behavior, and the shape and location of the lozenge-shaped openings of the expanded metal and the alignment of the webs can be selected depending on the influence desired. The corresponding uniform turbulence enables the cooling capacity of the flame barrier to be optimally utilized without excessively increasing the flow resistance. As well as making the flow through the other expanded metal perforated wall more uniform, the characteristics of the frame front, if applicable, are changed in such a way that no sparks form in closely confined areas, but rather distribution takes place over a larger area with the result that the heat absorption capacity of the flame barrier is better utilized and no local overloads are able to occur. The time taken for the flame front to pass through the valve is also thereby increased. The passing of any flames through the valve can thus be reliably prevented. Diesel and gas engines protected with the valve according to the invention can therefore also be used in hazardous areas, and/or complicated above-roof pressure and flame outlets are no longer necessary, and the non-hazardous relief of pressure into the working space is possible. The expanded metal of the valve construction provides greater mechanical strength, on the other hand, enabling even repeated explosions to be withstood without deformations occurring which adversely affect operation, the valve remaining fully effective and operational. This is of great economic significance as the overriding majority of ships today are built without redundancy and the failure of the one and only engine may have dire consequences.
The effect of influencing the flow for improved utilization of the cooling capacity of the flame barrier is revealed particularly clearly if at least one expanded metal wall is positioned immediately in front of the first flame barrier.
According to another optional feature of the invention, on the other hand, at least one perforated wall may be positioned immediately after the last flame barrier.
According to another optional feature of the invention, at least one flame barrier and a perforated wall may be positioned behind the valve seat. As a result the first pressure peaks are caught by the closure plate of the valve before they impinge on the first flame barrier and/or perforated wall, which are thereby better protected from damage.
In order to achieve a directed gas flow after its exit from the explosion relief valve, the perforated wall is preferably made of expanded metal and its webs are set in such a way that the gas flow emerging from the valve is directed at the surface of the space to be protected. This means that even in the most confined conditions, danger to operating personnel may be prevented to the greatest possible extent and without great effort.
With the advantage of structural simplicity, the saving of weight and the low space requirement, the valve behind the last flame barrier can be free of any deflecting devices for the emerging gas flow. On the other hand, if there is available space provision, the valve may be larger in size and thus be more reliable in operation and/or suitable for higher explosion pressures.
Advantageously, according to another optional feature of the invention, at least one flame barrier may be annular and permit throughflow over substantially 360xc2x0 and at least one additional perforated wall may be provided in an annular shape on the exterior or interior periphery of at least one flame barrier. This feature increases the effectiveness of the action to make flow more even and ensures the least possible load per unit area on the flame barrier and also on the other perforated wall.
To achieve advantageous weight and also size optimization and more economic production, at least one flame barrier may be made of aluminium or stainless strip steel.
A preferred embodiment of the present invention will be described in more detail with reference to the accompanying drawings.